1. Field of the Invention
The invention relates to stepped mold inserts, with which stepped microstructural bodies are manufactured, and a process to manufacture the stepped mold inserts. The present invention also relates to a process for economically manufacturing stepped microstructural bodies.
2. Discussion of the Related Art
Microstructural bodies manufactured according to the LIGA procedure have microstructures with lateral dimensions in the micrometer range at a height that can amount to several hundred micrometers. Generally the microstructural bodies are planar, i.e., the lateral dimensions of the microstructures are virtually constant over the entire height of the structure.
According to EP-184 608, bodies with column-like microstructures can be manufactured whose heights are different in two regions. In addition, one layer of a plastic, whose properties can be altered through x-radiation (resist material), is first partially irradiated through a structured mask, whereby the x-radiation penetrates through the entire thickness of the resist layer. The resist layer is subsequently irradiated again with X-radiation through a second structured mask, whereby the penetration depth of the radiation is less than the thickness of the resist layer and the irradiated regions are larger than during the first irradiation procedure. This process is fundamentally suitable for manufacturing microstructural bodies having more than two different structural heights. Each structural height requires its own irradiation step. For each irradiation step a separate mask is used that is to be positioned with high precision relative to the already irradiated regions of the resist layer. Thus, the expense is significantly increased and the yield is noticeably decreased.
In EP-253 066 a process for the manufacture of microstructural bodies with regions whose structural height varies is specified. A resist layer is irradiated once through a single mask, whose structure corresponds to the structure of the microstructural body (absorber structure) (deep x-ray lithography). The mask comprises a structured layer, which absorbs almost totally the x-radiation (total absorber layer), and at least one other structured layer, which absorbs only partially the x-radiation (partial absorber layer). The resist material is a plastic with a sharp lower limit dose, e.g., polymethyl-methacrylate. For the partial absorber layers, substances with varying absorptibility within the wavelength range of the x-radiation that is applied are used. The kind of partial absorber materials, their respective layer thickness, the spectrum of the x-radiation applied and the radiation dose are to be adjusted to the desired varying structural heights of the microstructural body. This procedure needs extensive calculations.